Chemical Evolution of Galaxies with Exponential Inflow of Metal-Poor Gas Some quick explanations of the applet's use:

Left hand panel = model input parameters

• timestep: 0.01 Gyrs will often suffice, as the age of the galaxy is covered by about 1000 time steps.
• the star formation rate is given as a function of the instantaneous gas mass by this simple relation: SFR = constant * (gas mass)^exponent
• accretion time scale: the rate of accretion of metal-free gas into into the galaxy is assumed to decline exponentially in time. The total amount of gas is one galaxy mass (Mgal) over 13 Gyrs.
• initial gas mass: this is the amount of metal-free gas in the galaxy at the beginning. The unit is Mgal ... therefore, the final total mass in the galaxy can be as large as (Minitial+Mgal)
• wind factor: there may be a continous outflow of interstellar gas. Its rate is assumed to be W = windfactor*SFR
• hitting the enter key while in a textfield - after changing the parameter value, for example - will start the next simulation

Right hand panel:

• clear plots: wipes all graphics
• start: start the simulation with the parameters as given on the left hand panel
• stop: halts the current simulation
• resume: continues with the halting simulation
• drag&zoom: click the button, then drag the mouse over that region of the plot which you want to zoom in. Then re-run the simulation
• unZoom: brings back the full view of the plot, but you have to re-run to restore the curve(s)
• clicking on the plot surface will display the x and y-values of that point
• the two Choices allow to select any of the simulation's variables to be used as x and y-values of the plot

The variables:

• time (in Gyr)
• gas (mass in units of Mgal)
• gas fraction = fraction of the total current mass in the form of gas
• log gas fraction: its decadic logarithm
• massive stars = fraction of current total mass in the form of stars more massive than 10 solar masses. These are about 12 percent of a stellar population (using Salpeter's IMF), they have a mean lifetime of 10 Myrs, and return 90 percent of their initial mass to the interstellar gas when they explode. (I use an approximate formulation ...) This prescription gives a stellar locked-up mass fraction of about a = 0.9
• low mass stars = fraction of current total mass in the form of stars that never die and which do not contribute to the production of metals
• SFR: the current star formation rate in units of Mgal/Gyr
• ACC/SFR = accretion factor = ratio of accretion rate and SFR
• SFR/ is the ratio of the instantaneous SFR to the past average one
• metallicity: is the abundance (by mass) of a primary element, viz. one produced with a constant yield, measured in units if this yield.
• effective yield: a closed-box model with the current gas fraction would give the current metallicity, if its yield was that value (we normalize to the true yield). This variable shows the efficiency of the model with respect to a closed-box model.